Method of making wall board



Oct. 31, 1933. D. DE F. CRANDELL METHOD OF MAKING WALL BOARD Filed Feb. 23, 1935 INVENTOR 6 m 1 UL ATTORNEYS Q Q Q Q II!1IIIIIIIIIIIII!III Patented Oct. 31, 1933 UNITED STATES METHOD or MAKING WALL BOARD Dean De Forest Crandell, Buffalo, N. Y., assignor to National Gypsum Company, Bufialo, N. Y., a corporation of Delaware Application February 23, 1933. Serial No. 657,847

8 Claims.

of a core overlaid with paper; and relates more particularly to a gypsum wallboard overlaid with an acid cover paper.

The principal object of the invention is to provide a wallboard which is inherently strong and inexpensive and of light weight and has a strong adhesive bond between its core and the covering paper which overlays its one or more faces. Numerous other objects of the invention and practical solutions thereof are disclosed in detail in the herein patent specification In the accompanying drawing:

Figure 1 is a fragmentary, vertical, longitudinal section through a continuous production machine adapted to commercially produce the wallboard of the present invention.

Figure 2 is a considerably enlarged, fragmentary, transverse section of a finished piece of wallboard made in accordance with the present invention.

Similar characters of reference indicate like parts in the several figures of the drawing.

My invention may be constructed in various manners and in wallboards and the like of different constructions, and the present application is therefore to be regarded merely as one organization which satisfactorily carries out the invention in practice. As here shown, the same is constructed as follows:

' Awallboard constructed in accordance with the present invention is adapted to be manufactured on a production basis on a machine such as that shown in Fig. 1.

The numeral 10 represents a suitably proportioned mixture constituted chiefly of water, macerated wood pulp and pulverized gypsum. This mixture is suitably fed upon the upper surface of a moving soak belt 11 which is suitably supported by a plurality of supporting rollers 12 and passes successively around the guide pulleys 13, 14 and 15. As said mixture passes under a caustic-solutionfeed pipe 16 it receives a supply of NaOI-I or other caustic or alkali solution, the amount fed being suitably regulated by a globe valve 1'7. To thoroughly and uniformly mix this caustic solution with the wood-pulp, gypsum mixture to form ahomogeneous core paste 18, a plurality of rotating agitators 20 are employed, each of the same being suitably mounted on a vertically journaled rotating head 21 driven by bevel gears 22 and 23, all of the bevel gears being driven from one common line shaft (not shown).

This core paste 18 is deposited in a continuous stream upon the upper surface of a lower cover This invention relates to a wallboard consisting paper 24, the latter being suitably supported upon the upper horizontal surface of a deck plate 25 and continuously supplied from a supply roll of paper 26 suitably mounted on a horizontal, transverse shaft 27. As this core paste 18 iscarried along forwardly upon the upper surface of the lower cover paper 24, it is prevented from spilling off the sides of said lower cover paper by a pair of edge plates 28 constructed and arranged in the usual and well known manner at opposite sides of the deck plate 25.

This lower cover paper 24 with its superincumbent layer of core paste 18 continues forwardly and passes between a pair of vertically disposed rollers 30 and 31, the former being the head pulley of a pre-drying belt 32 (supported intermediately its length by a plurality of supporting rolls 33) and the latter supplying to the upper surface of the core paste 18 a constant supply of upper cover paper 34. These two cover papers 34 and 24, together with the core 181 disposed between them, constituting the formed, but not as yet dried, gypsum wallboard.

The fabrication of the wallboard is now complete,-the remaining steps in its manufacture consisting of the usual and well known processes of cutting this formed and fabricated but not dried wallboard into suitable lengths and then passing the same through suitable drying kilns. The essence of the present invention is concerned with the chemical composition of the core paste 18 and of the cover papers 34 and 24,-- this chemical composition determining both the final strength of the bond between the core 181 and said cover papers (when the wallboard has been passed through the drying kiln), and also determining the weight, strength and pliability of the, core 181 itself and hence the finished wallboard as a whole,

Heretofore, the adhesion between the wallboard core and the cover papers has been obtained by the addition to the core of a relatively large percentage of starch. This starch unquestionably has a high value as an adhesive,- but, when employed in the manufacture of gypsum wallboard in the manner which has heretofore been common practice, a wallboard is produced which has the detracting characteristic of being relatively expensive (due to the relative- 1y high cost of the starch used) and also inherently heavy, weak and brittle.

' In the present invention, the percentage of starch required for proper adhesion between the core 181 and the cover-papers 10 and 16 is very markedly decreased, and the resulting wallboard at the same time rendered lighter, stronger and less brittle. This result is-obtained by very considerably reducing the percentage of starch in the core paste 18 and adding a suitable proportion of NaOH solution or other base or alkali solution, 1. e., a solution having an alkalinity value (pH value) greater thanthat of .water (which has a pH value of 7). With commercial costs as they are now, the alkali solution preferred is an NaOH solution, the amount used being .07%, this percent being based upon the weight of the wallboard when dried.. It would be somewhat moreaccurate to have this percentage based upon the weight of the dried core of the wallboard, but, for commercial production, a percentage based upon the dried wallboard has been found most convenient and hence has been used as the basis of measurement here.

Such an addition of alkali solution to the core paste has the following advantages:

A. It decreases the quantity of starch required and hence decreases the total cost of the finished wallboard.

' B. It increases the strength of the core and also the strength of the bond between said core and its cover papers, and hence increases the strength of the wallboard as a whole.

C. It increases the amount of water which can be advantageously used in the core paste and, hence, (by increasing the percentage of voids in the core, decreases the total weight of the dried and finished wallboard.

' D. It renders the wallboard more pliable.

E. It decreases the time required for the core to set.

The reason why the bond between the core 181 and its cover papers 24, 34 is increased by the addition of .07% of NaOH solution (or a suitable amount of other base or alkali solution) to the gypsum, wood-pulp mixture 10 is as follows: Commercial cover paper, is manufactured by.

adding sodium rosinate sizing to a suspension of macerated wood pulp in water in a paper mill beater and then "setting said sizing in the-paper fibers by adding alum solution. The latter has a pH value (alkalinity value) of approximately 3.3 and hence is very acid and causes the resulting cover paper to be acid.

This rosinate sizing is necessary in the manufacture of the paper in that it prevents an excessively free movement of the water through the paper while it is lying on the'travelling "screen, andthereby prevents softening and "scufling of the paper. As far, however, as the use of the paper as a cover paper-for a gypsum wallboard is concerned, this sizing has, in the past, prevented a proper bond between the cover papers and the gypsum, wood-pulp core. This has been due to the fact that said sizing has prevented the core paste fromproperly penetrating into, or being absorbed by, the cover papers, so as to be able later to harden therein and thereby form a strong bond between said coreand its cover papers.

In the present invention, the NaOH solution in the core paste, being highlyalkaline is enabled to dissolve the sizing of the inner surface of each cover paper, evenin the presence of the acid alum of the paper, andis able, thereby, to open up the interstices or pores in the inner surface of said paper and to allow the core paste to pass thereinto and to thus form a strong bond between the core 181 and the, cover papers 24, 34. This is.

shown graphically in Fig. 2 in which. is illustrated, in conventionalized fashion, how the NaOH solution roughens and penetrates the inner surfaces of the cover papers by dissolving the rosinate size in the presence of the alum and thereby enables the core paste to penetrate into said cover papers.

In addition to this increasing of the bond strength between the core 181 and its cover papers, the presence of the alkali solution in the core -paste 18 renders the finished (dried) core 181 lighter, stronger and more pliable, beside reducing the amount of starch required and hence reducing the production cost of the finished wallboard.

The foregoing is not mere theory, the fact having been definitely established that the reduction in the percentage of starch normally required in the core paste 18 and the addition of a base or alkali solution thereto, very decidedly increase the strength of the resulting wallboard, both as to the core itself and also the bond between said core and its cover papers, and also renders the wallboard lighter, and more pliable and less expensive than gypsum wallboards manufactured in the usual way without any addition of alkali solution to the core paste.

Broadly considered, the present invention provides a wallboard having a superior type of core and superior bond between said core and its one or more cover papers, and it is obvious that these characteristics are related to each other so long as there is a chemical action between the core paste and the inner surface of the cover papers. Whether this is accomplished by a chemical ingredien't in the core paste which attacks the cover papers, or a chemical ingredient in the cover papers which attacks the adjacent portion of the core paste is immaterial as far as the present invention is concerned. There are, however, two methods of making wallboard and also within the I scope of thepresent invention, in which there is no chemical action between the core paste and the cover paper. One such method is to treat the inner surface of the cover paper with a suitable size-dissolving or other roughening reagent prior to bringing said paper into contact with the core paste 18. Another such method is to mechanically roughen the inner surface of each cover paper prior to bringing it in contact with said core paste. Neither of these methods are considered 128 and the core, and, in such case, obviously, the

core paste may differ markedly from that specifically disclosed herein and stillenable a strong bond to be secured between the cover papers and the core as a consequence of the pre-treatment of said cover papers. The invention is desired therefore not to be confined to the use of an alkali solution with a gypsum core paste and acid cover papers, but to include any wallboard in which the core of said wallboard penetrates into the interstices of the cover papers, or, vice versa, in which projections of portions of the cover papers penetrate into the core.

I claim as my invention:

1. The process of making a wallboard consisting of... overlaying a cover paper with a core paste having an alkalinity equivalent to more than .03% of-sodium hydroxide.

.2. The process of making a wallboard consisting of overlaying an acid cover paper with a core paste having analkalinity equivalent to I more than 113% of sodium hydroxide.

3. The process of making a wallboard consisting of overlaying a rosin sized cover paper with a core paste having an alkalinity equivalent to more than 03% of sodium hydroxide.

4. The process of making a wallboard consisting of overlaying a cover paper with a gypsum core paste having an alkalinity equivalent to more than .03% of sodium hydroxide.

5. The process of making a wallboard consisting in overlaying an acid cover paper with a gypsum core paste having an alkalinity equivalent to more than 93% of sodium hydroxide.

d. The process of making a gypsum wallboard consisting in overlaying an acid, rosin sized cover paper with a gypsum, woodpulp core paste containing over" 93% of sodium hydroxide.

'7. The method of making wallboard consisting of preparing a core paste; and adding to said paste a, material which has a pH of more than seven, the amount added being equivalent in alkalinity to more than .03% of sodium hydroxide; and covering a layer of said paste with a cover paper which has a pH of less thanseven.

8. The method of making wallboard consisting of preparing a core paste consisting chiefly of gypsum; adding to said paste a solution of an alkali equivalent in alkalinity to more than .03% of sodium hydroxide; and covering a layer of said paste with a cover paper' whose sizing has a pH of less than seven.

DEAN DE FOREST CRANDEIL. 

